As such a plasma actuator, a sheet plasma actuator illustrated in FIG. 40 is typically known, for example. In this actuator, a front surface electrode 52 and a back surface electrode 53 are provided on the respective surfaces of a plate insulating body 51, which is made of a resin, a ceramic or the like and serves as a dielectric, such that the insulating body 51 is sandwiched between the front surface electrode 52 and the back surface electrode 53. When the front surface electrode 52 and the back surface electrode 53 are connected to an AC power source 54 and an AC electric field is generated, the plasma actuator generates a plasma jet 56 from an edge 55 of the front surface electrode 52 along the front surface of the insulating body 51.
The thus-generated surface plasma guides the neighboring gas to generate an induced gas flow 57. Accordingly, studies have been made to effectively apply the effects thereof in controlling the lifting power of wings and the like.
According to an exemplary study, as illustrated in FIG. 40(d), a surface plasma generator 59 as described above is provided on a front surface of a wing 58 at a position where the air flow tends to be separated from the wing surface. In the example illustrated in the same drawing, upper electrodes 52 are linearly aligned on the front surface of the wing.
The surface plasma generator 59 in use generates surface plasma from the edges 55 of the front surface electrodes 52 in accordance with the principle described above, and a plasma jet is generated. The generated plasma jet affects the gas flow flowing around the front surface of the wing 58 in accordance with the principle of the induced gas flow generation, and thus can prevent the separation of the gas flow which tends to take place at this position.
In particular, the surface plasma generator, which does not include any mechanical operative portions, is hardly damaged, and thus can be stably operated for a long time.
As described above, the plasma actuator is employed as a device for preventing the separation of the wing surface gas flow. In addition, in view of the characteristics of the plasma actuator, such as a characteristic that no operative portions are included and a characteristic that the plasma actuator is small and light-weight, the plasma actuator has been developed for preventing the separation or turbulence in various apparatus using fluid flow, or as a propulsion source for flight vehicles for flying through outer space.
Particularly as illustrated in FIG. 40(a), in the plasma actuator, the AC power source 54 can be controlled by a controller 60. Further, a sensor 61 detects the gas speed or the temperature. Based on the detection signal, the controller 60 controls the AC power source 94. By this operation, the plasma actuator generates the surface plasma corresponding to the conditions at this time.
According to the example illustrated in FIG. 40(b), at this time, an AC pulse is output as the control signal for 1/15 second. Then, after the pausing of 13/30 second, the same AC pulse is output. By conducting a duty ratio control to increase the pulse supply time as illustrated in FIG. 40(c), a stronger plasma jet is generated and a faster induced gas flow is generated around the plasma jet.
Patent Literature 1 discloses a technique to stably generate surface plasma of high speed by suitably setting the rising steed of a voltage applied to electrodes of a plasma actuator. Patent Literature 2 discloses a plasma actuator stably operable even under high temperature environment. Patent Literature 3 discloses a technique to apply a plasma actuator to an ozone generator. Patent Literature 4 discloses a technique to apply a plasma actuator to an anti-icing device.
In addition, Patent Literature 5 mentioned below discloses that the generation of a noise gas flow is reduced by accommodating primary components of a pantograph in a collector shoe shaped like a hollow box. Further, Patent Literature 6 mentioned below discloses that the generation of a noise gas flow is reduced by covering an arm of a pantograph with a cover.
Patent Literature 7 mentioned below discloses that a blade is protected from high temperature by injecting compressed air from an end of a turbine blade toward a tip clearance, and that the optimum tip clearance is maintained by providing a plate configured to reduce a tip clearance vortex.
Non-Patent Literature 1 mentioned below discloses the effects obtained by providing a plasma actuator to a distal end of a turbine blade lattice, by means of visualizing the flow within the tip clearance and measuring the pressure at the outlet of the blade lattice. According to this literature, the plasma actuator suppresses the generation of leakage vortex and reduces the loss by 9% at maximum.